1. Field of the Invention
The present invention relates to an actuator for driving a to-be-driven object with the help of extension/contraction of a shape memory alloy.
2. Description of the Background Art
An actuator is known which drives a to-be-driven object by extension/contraction of a shape memory alloy (SMA) wire or foil, or the like. In manufacturing such an actuator, the initial state in which SMA is mounted is examined, where the initial position of a to-be-driven object in the actuator problematically varies due to variations in tension control when mounting the SMA, tension variations resulting from the state of how the SMA is mounted, and the like.
To overcome such drawbacks, an actuator provided with an adjusting mechanism for adjusting the initial position of a to-be-driven object has been presented (e.g., Japanese Patent Application Laid-Open No. 10-160997 (1999)).
By the technique presented in JP10-160997, however, elongation of SMA is not stable due to tension variations at mounting. Under such condition, even by applying a predetermined tension to SMA so as to adjust the tension applied thereto, the tension on SMA varies at extension/contraction caused by the initial heating and cooling, which in turn displaces the initial position of a to-be-driven object.